The present invention relates to centrifugal pumps, and more particularly to centrifugal pumps used for transporting slurries and other abrasive-containing fluids.
A centrifugal pump consists basically of a rotatable impeller enclosed by a collector or shell. As the impeller is rotated, it generates velocity head at the periphery of the shell. The shell collects the velocity head and converts it to a pressure head. There are many configurations within the framework of this basic design. In one common configuration, the flow enters the shell at a point adjacent to the center of the impeller, referred to as the xe2x80x9ceyexe2x80x9d of the impeller, while the discharge of the shell is located at a point tangent to the shell""s outer periphery.
The magnitude of the head is largely determined by the impeller diameter, and the flow is mostly affected by the width of the pump and the size of the internal section area. The shell and the impeller tend to work like two nozzles in series, with the impeller generating, and the shell collecting, the head. A change to either will affect the head and the flow. Because both can be varied, more than one combination of variables of impeller and shell dimensions can achieve the same effect.
The magnitude of the peak efficiency is largely determined by the efficiency of the impeller and the wetted geometry in generating and collecting the head and flow. The location of the best efficiency point (BEP) is affected in large part by the magnitude (width and depth) of the hydraulic sections. Larger hydraulic sections cause the location of the BEP to move to higher flows.
With regard specifically to slurry pumps, these pumps are subject to high wear due to the abrasive effect of particles in the slurry, which through impact and friction erode the various pump surfaces.
As a consequence, slurry pump hydraulic sections have tended toward sizes larger than absolutely necessary in order to keep velocities down, since velocity is a large factor in the wear process. Decreased wear, however, comes at the expense of pump efficiency, since the pump is not operated at or near the BEP. This results in overall increased costs of operation. Thus, there is a need in the art for slurry pumps with increased wear characteristics.
The present invention provides a centrifugal pump having inlet blade angles set to an angle which takes into account the velocity of the solids moving within a slurry steam to reduce the wear on the centrifugal pump. Slurries are often striated where the lower half of the slurry stream contains a greater percentage of solids than the upper half. The solids in the lower half have a velocity which is significantly less than the liquid component of the remaining slurry steam. Thus, by optimizing the inlet blade angle to correspond to the velocity of the slower moving solids, wear on the centrifugal pump can be significantly reduced.
In an embodiment, the present invention provides a centrifugal pump for pumping a slurry containing a solids fluid mixture. The centrifugal pump has a shell with a central axis that includes a front wall and a spaced back wall, a generally continuous outer side wall extending between the front wall and the rear wall and a discharge nozzle disposed tangentially with respect to the side wall. Additionally, a suction inlet is included that is defined in the front wall about the axis for allowing the slurry to enter the shell and an impeller is rotatably supported within the shell about the central axis. The impeller includes a plurality of vanes, wherein each vane has an inlet angle and an exit angle. The vane inlet angles provide a substantially shock-free entry for the solids fluid mixture entering the impeller.
Furthermore, the present invention provides a centrifugal pump for pumping a slurry containing a solids fluid mixture. The centrifugal pump has a shell with a central axis that includes a front wall and a spaced back wall, a generally continuous outer side wall extending between the front wall and the rear wall and a discharge nozzle disposed tangentially with respect to the side wall. Additionally, a suction inlet is included that is defined in the front wall about the axis for allowing the slurry to enter the shell and an impeller is rotatably supported within the shell about the central axis. The impeller includes a plurality of vanes, wherein each vane has an inlet angle optimized for providing a substantially shock-free entry of slurry into the pump relative to a velocity profile of the solids contained within the lower half of the slurry profile.